So grateful for all the input and different perspectives. You have provided much needed direction and given me ideas to think about and options to research. To clarify my intimidation--I am very excited about the opportunity to plan a trip like this but with cities/towns that are new to us in multiple countries, it obviously requires a fair amount of research. In a perfect world, several less ambitious trips might make more sense but my husband's bucket list is focused on exploring areas of the U.S. with our RV. I consider it a blessing to look forward to doing both. I hope we make other trips to Europe in the future but if not, this trip will be memorable in itself.
Going back over some of the tentative itinerary with specific follow up from your helpful comments:
London--We are flying 1st class and arrive @ 0700 so I think we will be rested enough to sightsee that day. Hop On/Hop Off bus for that day to get an overview? Maybe 2 more days in London broken up by one day trip with the total # of days there still 4? I really like the idea of a trip to the English countryside. I would like to choose a small town that is not too expensive to travel to and doesn't require too much travel time. On the other hand, if there is a place that is a must-do but requires a little more effort, that is possible.
Brussels--Seems to be a consensus that 4 nights is too much and that there are better options. It looks beautiful at night so maybe after taking the Chunnel from London, we could spend the rest of that day and one night in Brussels, then spend 2 more nights in Bruge, Ghent, or Antwerp.
Amsterdam--I actually planned to spend 5 nights in Amsterdam but as a home base for day trips to small towns. Maybe 2 days in the city itself to see Anne Franke House, etc. and then day trips. Not a fan of switching hotels every day so that seemed like a viable option. Maybe better to stay in Haarlem instead and day trip from there? I would absolutely love to go to Giethoorn (it has been on my Pinterest board for a long time!) but not sure if it is too far from Amsterdam. I will do more reading on the small towns in the NL to see which we might enjoy (canals, windmills, hopefully flowers, local markets, cheeses, ethnic food, biking, etc.)
Berlin--Everyone I know who has been there liked it. Someone suggested renting bikes b/c it is spread out. Because of its crucial place in history, there are some landmarks we would like to see but now questioning whether 4 nights is too much. We really liked Munich but I am beginning to wonder whether Berlin should be part of our itinerary and if not, what other places make sense logistically. I am not familiar with the towns mentioned as possibilities on the way to Berlin but will check them out. So many decisions!
Prague--We can do a free 48 hr. layover enroute from Berlin to Vienna--thus the 2 night stay. It wouldn't be the end of the world if the stopover wasn't free but truthfully, it was added because of the layover perk.
Vienna--Like almost anything, some people love it and some are less impressed. Appreciate the suggestions for day trips from Vienna. I will do some reading about Melk. I should have mentioned before that we previously stayed in Salzburg (from Munich) and loved it but at this point, I am trying to seek out places not yet explored. Thank you for the suggestion to day trip to Bratislava--I am pretty clueless about it but will definitely look into it!
Budapest--This is the fixed endpoint for our trip. I am happy with our Business class flights back to MI from there and really don't want to pay a change fee. It looks like a gorgeous city.
This trip has changed from originally thinking about a shorter trip (Amsterdam-Copenhagen-Berlin) without even a remote thought of destinations like Budapest. Your suggestions encourage me to keep an open mind about what would make this a great travel experience for us. Please continue to share your thoughts!